Motor graders are used primarily as a finishing tool to sculpt a surface of the earth to a final arrangement. Typically, motor graders include a work implement, such as a surface-altering blade, that is movably connected to a front frame of the motor grader by a pair of independently controlled hydraulic actuators. The hydraulic actuators are mounted on either side of the front frame of the motor grader and operated independently, and can be extended or retracted to lower or raise the respective ends of the blade relative to the corresponding sides of the front frame. The blade height may be controlled manually or automatically.
U.S. Pat. No. 7,588,088 relates to a control system for controlling the blade position. The control system includes a first hydraulic actuator position sensor for determining the extension of the first hydraulic actuator. The control system further includes a controller that is responsive to a control input specifying a desired height and cross slope of the blade, to the first hydraulic actuator position sensor, and to an inclinometer output indicating the inclination of the blade along its length with respect to horizontal. The control provides valve control signals to a first and a second hydraulic valve to control the flow of hydraulic fluid to the first and second hydraulic actuators, which raise and lower respective ends of the blade. The control provides a first valve control signal to the first hydraulic valve in dependence upon the desired height specified by the control input, and the control provides a second valve control signal to the second hydraulic valve in dependence upon the inclinometer output, and the cross slope specified by the control input. Moreover, when the blade is to be moved upward or downward with the retraction or extension of the first actuator, the controller provides the second valve control signal to the second hydraulic valve in dependence upon the first hydraulic actuator position sensor, such that the second hydraulic actuator retracts and extends with the first hydraulic actuator, maintaining the cross slope angle of the blade as a constant.